Water pollution: a very short introduction

Water Resources Surface water Groundwater Desalination Treated wastewater Treated wastewater... Water ResourcesAbout 2.2 billion people in developing countries lack access to safe dri

WATER POLLUTION

Evaporation 505x10 3 km 3

Evapotranspiration 72x10 3 km 3

Precipitation on land

119x10 3 km 3

Precipitation on sea 458x10 3 km 3

Runoff 47x10 3 km 3

The Hydrologic

Cycle

Water Resources

Surface water Groundwater Desalination Treated

wastewater Treated

wastewater

Water Resources

About 2.2 billion people in developing countries lack access to safe drinking

water.

About 2.7 billion people in developing countries lack access to safe sanitation services.

Water Use

Domestic Industrial Agricultural

0 20 40 60 80 100

Income level

Industrial Agricultural

Water withdrawals by sector in low, mid and high income countries (Environmental Science: A Global Concern, W.P Cunningham and B.W Saigo, 3rd Ed Wm Brown Pub © 1995)

Agricultural Items

Water Usage

Water pollution

Physical

Chemical

Biological

Radiological

•Solids

•Pesticides

• Thermal Pollution

Causes a drop in the dissolved oxygen due to higher metabolic rate and lower DO solubility at higher temperature

• Solids

salinity)

and anions present expressed in mg/L

• Hardness

Hardness Description meq/L mg/L as CaCO 3

Moderately hard

) meq /

mg ( X of weight Equivalent

) meq /

CaCO mg

( 50 )

L / mg ( X of ion Concentrat CaCO

as X

of

L

3

×

=

number equivalent

weight molecular

or Atomic weight

Hardness classification

of water

Symbol Atomic or

molecular weight

Equivalent number

Equivalent weight

(mg/meq)

• Heavy Metals

• Nutrients

• Pesticides

fungicides, etc

• Volatile Organic Compounds (VOCs)

Biochemical Oxygen Demand (BOD)

to oxidize organic wastes

Organic matter + O2 COMicroorganisms 2 + H2O +………

BOD

CBOD

Carbonaceous oxygen demand

NBOD

Nitrogeneous oxygen demand NBOD

Nitrogeneous oxygen demand

Case 1: No Dilution

BOD5 = DOi - DO5

Dissolved oxygen after

5 days

Dissolved oxygen

initial

5 days

at 20 o C

Sample

DOi

Sample

Case 2: Diluted sample with blank free from organics

5 days

at 20 o C

Diluted sample

DOi

Diluted

sample

V V

V P

+

=

P

DO

DO

5

−

=

Dilution factor

) P 1 ( )

DO DO

( )

DO DO

( BOD5 i − 5 dilutedsample − i − 5 dilution −

=

Case 3: Diluted sample with blank that has organics

5 days

at 20 o C

Diluted sample

DOi Diluted

sample

5 days

at 20 o C

Dilution water

DOi Dilution water

How to select P?

Two conditions have to be met:

(i) DO5 > 2 mg/L

(ii) DOi-DO5>2 mg/L

Example 5.2

P

) P 1 ( )

DO DO

( )

DO DO

( BOD5 i − 5 dilutedsample − i − 5 dilution −

=

A test bottle containing dilution water has its DO level drop by 1.0 mg/L in a five-day test A 300-ml BOD bottle filled with 15 ml of wastewater and the rest dilution water experiences a drop of 7.2

Solution

05

0 285 15

15 V

V

V P

dilution sample

+

= +

=

L / mg

125 05

0

) 05 0 1 )(

0 1 ( ) 2 7 (

Problem 5.4 with modification

of approximately 250 mg/L If the initial DO of a mix of dilution water and wastewater is 8 mg/L What is the best dilution factor to

Solution

(i) DO5 > 2 mg/L

(ii) DOi-DO5>2 mg/L

7 41 / 1

P P

2 8 250 P

DO DO

125 / 1

P P

2 250

P

DO DO

P

DO DO

5

−

=

Example 6.4

A groundwater sample has 100 mg/L Ca and 10 mg/L Mg Classify the water from a hardness point-of-view

Solution

) meq /

mg ( X of weight Equivalent

) meq /

CaCO mg

( 50 ) L / mg ( X of ion Concentrat CaCO

as X

of

L

3

×

=

250 )

meq /

mg ( 20

) meq /

CaCO mg

( 50 ) L / mg ( 100 CaCO

as Ca

of

L

41 )

meq /

mg ( 2 12

) meq /

CaCO mg

( 50 ) L / mg ( 10 CaCO

as Mg

of

L

water is classified as hard